Waterway_Hydraulics_Memo.pdf
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- MT DOT 569 (3), North of Moose Creek North
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- 69056718B000024
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Memorandum
Western Federal Lands Highway Division 610 E. Fifth Street
Vancouver, WA 98661-3801
CALIFORNIA CREEK BRIDGE
WATERWAY DESIGN HYDRAULICS MEMO
To: Keith Wong, WFLHD Project Manager From: James Neighorn, P.E., WFLHD Hydraulics Engineer Date: September 15, 2016 Project: MT DOT 569(3) – North of Moose Creek North
Background
Montana Department of Transportation is replacing the bridge at California Creek. Western Federal Lands Highway Division (WFLHD) is designing the bridges. Recommendations for the initial waterway width, skew angle, and minimum bridge low chord elevations.
Recommendations
Minimum low chord elevation (project datum) 6257.0 feet.
32-foot waterway width, assuming spill-through abutment with 2(h):1(v) slopes, and 20-foot channel width.
The angle between bridge centerline and channel centerline is 45 degrees. Abutments and bridge deck constructed using a 45 degree skew may be difficult and increase cost. Consider using a 30 degree skew and lengthening the bridge to avoid constructing the new abutments over the existing bridge abutments.
The centerline of channel crosses the centerline of road at Northing 650912.75, Easting 1075237.02.
Utilize riprap class 2, 2 feet thick to protect the embankment slopes.
Attachments: Bridge Hydraulics & Scour Analysis Summary
To: By: James Neighorn, P.E.
Project: MT DOT 569(3) - North of Moose Creek North WFLHD Hydraulics Engineer
Bridge: Date:
BRIDGE STRUCTURE SUMMARY
Low Chord Elevation 6257.0 feet (Project Datum)
Minimum Design Freeboard 3.0 feet above the 50-year flood (Needed for woody debris passage.
Stream Bottom Elevation 6251.4 feet and extensive beaver activity.)
Clearance to Stream Bot. 5.6 feet
Waterway Width 32 feet
Skew 45 degrees relative to stream
Bridge/Stream CL Sta Bridge Start Bridge End
Abutment Type Spill-through, clear span, no piers.
HYDRAULIC & HYDROLOGIC SUMMARY
Flood Frequency Yr 2 10 25 50 100 500
Exceedance Probability % 50 10 4 2 1 0.2
Discharge cfs 93 278 322 369 487
Modeled Water Surface Elevation *** Elev 6253.1 6253.8 6254.0 6254.1 6254.4
Elevation Datum Conversion Ft 0.0 0.0 0.0 0.0 0.0
Project Water Surface Elevation Elev 6253.1 6253.8 6254.0 6254.1 6254.4
Clearance above WS Ft 3.9 3.2 3.0 2.9 2.6
Existing Water Surface Elevation *** Elev 6253.6 6253.8 6255.0 6255.3 6255.6
Predicted Flood Rise Ft -0.5 0.0 -1.0 -1.2 -1.2
Design Flow Velocity Ft/sec 2.4 3.8 4.1 4.4 4.9
Scour Base Elevation (Channel Thalweg) Elev
Contraction Scour Depth Ft
Stream Degradation Depth Ft
Left Abutment Scour Depth Ft
Right Abutment Scour Depth Ft
Total Left Abutment Scour Elevation Elev* 0.0 0.0
Total Right Abutment Scour Elevation Elev 0.0 0.0
Pier Scour Depth Ft NA NA
Total Pier Scour Elevation Elev* NA NA
Streambed material grain size (inches) D100 D50 D15
Scour Design Basis
Project Elevation Datum
RECOMMENDED SCOUR COUNTERMEASURES
Type
Top Elevation 2655.0 Slope (H:V) 2:1
Bottom Elevation 2649.4 Toe Width (Ft) 4
Thick (Ft) 2 min Toe Thickness (Ft) 2
Riprap Design Basis
NAVD88 GEOID99
Riprap, Class 2 (FP-14)
HEC-23
BRIDGE HYDRAULICS & SCOUR ANALYSIS SUMMARY
Keith Wong, WFLHD Project Manager
9/15/2016California Creek
California Creek Bridge Hydraulics Summary.xls
California Creek
FOUNDATION SUMMARY
GEOTECHNICAL SUMMARY
STREAM PLAN & PROFILE STABILITY
The active channel width is 20 feet. OHW is approximately 1.5 feet. Stream gradient is 1.5 percent upstream and downstream. There is extensive beaver activity upstream which has caused the creek to migrate and avulse over a 300 foot wide flood plain. No beaver activity was observed immediately downstream. However, there is potential for beavers to create dams downstream of the bridge. This can potenially increasing water levels up to 1 to 2 foot at the bridge.
Large woody debris recruitment and transports potential is low. Debris flow potential is low. Banks are heavily vegetated and moderately stable. The stable floodplain banks limit channel migration. The cobble and gravel bed appears to be stable with a moderate to low potential for degradation.
To be completed.
To be completed.
California Creek Bridge Hydraulics Summary.xls
N
PLAN
ELEVATION
Q Vel.
500Q
100Q
50Q
2Q
SLOPE PROTECTION
WS ELEV.
SCALE IN FEET
4020010
TYPE: Riprap
F lo w proposed channel
Bottom edge of stream channel
Centerline proposed
El. = 6257.0
Min. low chord
Placed Riprap, Class 2
El. 6255.0
El. 6249.4 centerline
El. = 6251.4 @ road
Proposed channel bottom at road centerline
Existing ground
El. = 6254.0
50-yr WS
Centerline
Proposed Roadway
DEPTH: 2.0 ft.
SLOPE: 2(h):1(v)
)500); --- ft. (Q100TOTAL SCOUR EL: --- ft. (Q
STATE PROJECT
NUMBER
SHEET
MT
C a li fo r n ia C r e e k B r id g e P r e li m in a r y L in e a n d G r a d e .d g n
I n t_ ft
D
C h e c k e d b y
J .N e ig h o r n
D e s ig n e d b y
PLAN AND PROFILE
CALIFORNIA CREEK BRIDGE
0 50 100-50-100-150
CLASS: 2
TOP EL.: 6255.0 ft.
BOTTOM EL.: 6249.4 ft.
REMARKS: Scour to be determined.
at road centerline
Approximate finish grade
6254.4
6254.1
6254.0
6253.1
5.9
5.1
4.7
2.4
4'
B o tt o m W id th
C h a n n e l
F lo w
DOT 569(3)
CL
Channel Bottom El. = 6251.4
N 650912.75, E 1075237.02
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